Newsletter

Postdoctoral fellow leads physics lectures on the mysteries of neutrinos

Twice every year, the University of Chicago’s Enrico Fermi Institute sponsors the Arthur Holly Compton lecture series, which provide the public an inside look at the questions about the universe with which the institute and its scientists are grappling.

The series is named for pioneering University of Chicago physicist and Nobel laureate Arthur Holly Compton, who demonstrated that light can be both particle and wave. Compton also directed the Metallurgical Laboratory, where Enrico Fermi and his colleagues produced the first controlled nuclear chain reaction in 1942.

The subject of this spring’s series, delivered by Grainger Postdoctoral Fellow Andrew Mastbaum, is the neutrino: the wiliest of all the particles in the universe. These tiny particles zip around and through us all the time, but they remain mysterious—yet they may be the gatekeepers to some of our most fundamental questions about the universe, from what makes the sun shine to why we exist at all.

Mastbaum answered a few questions for UChicago News.

Why do you study neutrinos?

Oh, neutrinos are where the party’s at. Everyone’s trying to find some kind of physics outside the Standard Model—something that’s outside of our current understanding of particle physics. And in neutrinos there’s all kinds of open questions and anomalies that our experiments have found. I feel like the time is right for discovery in one of those areas.

What are some of the neutrino experiments you’re working on?

I work on two experiments. At Fermilab I’m involved with the Short Baseline Neutrino Program, where our goal is to measure whether there’s some additional type of neutrino beyond the three ones we know about. The other is SNO+ in Ontario, Canada, which is located underground in a mine. It looks at neutrinos coming from the sun, which helps us understand how the sun works as well as how neutrinos work. But the main goal is to measure something called neutrino double-beta decay, which would only happen if a neutrino is its own antiparticle.

If you could find the answer to one of the questions about neutrinos, which would it be?

I think the question about whether neutrinos are their own antiparticles is really of fundamental significance. Among the known particles of matter, only neutrinos can get away with this, and it will be very interesting to see if that’s how Nature works. And that could also open the door to neutrinos being the solution to other problems—like the existence of the universe that’s full of matter and not antimatter.

So which one are you hoping for—it is or it isn’t its own antiparticle?

It’s so cool either way. If it is, that’s really interesting and feeds into this matter/antimatter symmetry. And if it’s not, then it suggests there’s something that actually differentiates neutrinos and antineutrinos that we don’t know about. So then there’s some fundamental symmetry of nature that we haven’t discovered yet.

But, if you pressed me…. I’m rooting for they’re their own antiparticles.

How would that affect physics?

The Standard Model, our main theory of particle physics, has evolved a bit over the years as we discover new things like neutrinos having mass, and add it in. But to make neutrinos their own antiparticles requires some bigger changes, and would be a strong hint that there is a some bigger-picture theory we don’t have yet, beyond the Standard Model.

When you started planning the lectures, what was something you hoped to get across?

One thing I wanted to communicate is this really interesting dichotomy with neutrinos. There’s so much we don’t understand about them, and so they’re really interesting to study in their own right to understand the universe; but in the meantime, because they’re so unique, we can use them as a probe. For example, they can help us see inside the sun, more or less, because the neutrinos come straight from the reactions in the core of the sun, while sunlight only tells us about what’s going on at the very outer surface. So we can use them to study physics out there in the universe even if we don’t fully understand the neutrinos themselves.

There’s a lot of very notable people who have done this before me, and it’s a real honor to be a part of that. And I think it’s a really cool opportunity to share some of the research we do—to share what the big open questions are, and what keeps neutrino physicists up at night. It’s really exciting stuff, and it’s great to be able to share that.

A syllabus and slides from past lectures are available at Mastbaum’s website. Funding for the free lectures is provided by the Enrico Fermi Institute; additional support from lecture attendees is welcomed.